This invention pertains to Global Positioning System (GPS) radios, in general, and to power conservation in GPS radios in particular.
Power conservation is an important function in various radios. It is particularly important with battery powered radios such as Search and Rescue (SAR) transceivers of the type used in the location and rescue of crews of downed aircraft and in other search and rescue or retrieval activities.
Modern SAR transceivers include a GPS receiver module. The GPS module is used to precisely identify the location of the transceiver and/or to provide precise time of day indications for establishing rendezvous with rescuers. The GPS module automatically determines the location of the transceiver and the SAR transceiver may transmit the location of the transceiver in response to interrogation signals from an interrogation transceiver carried on a rescue vehicle, or may transmit the location information on a periodic basis. Such transceivers may be triggered into operation by an incident switch which is used to sense the occurrence of an event for which the SAR transceiver should be activated. The transceiver may have to operate over an extended period of time before a rescue is possible. It may be many hours, if not days, before a rescue operation may be implemented and successfully completed. Further, in the presence of interfering signals, the GPS receiver may need to implement various and more sophisticated techniques for ascertaining its precise location. Such additional techniques typically consume more power.
Hence, there exists a need for a GPS receiver with SAR capability having the ability to accurately and precisely determine it location, even in the presence of interfering signals, while efficiently managing its overall power cosumption.